A crystal resonator includes a crystal element (also referred to as a “crystal blank”) interposed between an electrode pair. Because a crystal element may be a piezoelectric body, it changes shape when a voltage is applied. As a result, the crystal oscillator causes the crystal resonator to vibrate at its natural frequency. The crystal oscillator connects the electrodes of the crystal resonator using a conductive adhesive on electrode pads in a package. The electrode pads support the crystal resonator inside the package of the crystal oscillator. In other words, the conductive adhesive provides both electrical connection and mechanical support, without interfering with the natural frequency of the crystal resonator.
As a technique using a conductive adhesive, a technique in which a laser beam is used in a method of fabricating an infrared sensor has been proposed. According to this method of fabricating an infrared sensor, a pyroelectric base material having terminals on the front and back sides is disposed on a conductive plate, and the conductive plate is irradiated with a laser beam to scatter conductive material so that it attaches to the side surfaces of the pyroelectric base material. In this way, the infrared sensor is fabricated by attaching the conductive material to the side surfaces of the pyroelectric base material and causing the terminals on the front and back to short-circuit.
In the fabrication process of a crystal oscillator, a conductive adhesive is applied on an electrode pad inside a package of a crystal oscillator, and a crystal element is disposed on the conductive adhesive. The precision of the vibration of a crystal resonator is largely influenced by the amount and surface area of the conductive adhesive. Since the conductive adhesive is prepared through a mixing process carried out mechanically or manually, the viscosity of the conductive adhesive varies. For example, when a conductive adhesive having a viscosity lower than a predetermined value is applied on an electrode pad, the conductive adhesive runs off the electrode pad, causing the application area of the conductive adhesive to increase. The application area of the conductive adhesive also increases when the amount of conductive adhesive applied increases. In this way, an increase in the amount and/or the application area of the conductive adhesive influences the natural frequency of the crystal resonator. Moreover, the conductive adhesive that runs off the electrode pad causes short-circuiting of other electrode pads, and prevents the crystal resonator from receiving a predetermined voltage.
The size of an electrode pad has been reduced in response to the miniaturization of semiconductor chips; therefore, the conductive adhesive easily runs off the electrode pad. The run-off of the conductive adhesive from an electrode pad reduces the yield of products that are fabricated by applying a conductive adhesive on an electrode pad.